Some thoughts on thermal bridging around windows and doors in simple structures

ircoha

Following on from some of the comments by sinnerboy and others in this thread to whom I am obliged,
http://www.boards.ie/vbulletin/showthread.php?t=2055235906,

I have been giving some consideration to the issues around thermal bridging around opes.

If one accepts that any form of quality control on cavity walls, ( filled, partial filled, pumped etc) is problematic I looked at using either hollow 215mm blocks or even solid 100mm on flat and see what might work.

This design would work best in a building where you have 4 external walls with no internal walls tied into the external walls: eg garden studios and simple extensions.

The attached sketch shows one possible scenario on which I would welcome some comments.

The advantages for me include
1 the block work is simple, fast and std lintels etc can be used.
2 no messing with insulated dpc, closer blocks, cavity insulation etc.
3 you dont cover the window/door frames with the composite board.
4 The insulation work can be done once the building is roofed.

I appreciate there are issues around using these sorts of boards with toxic gasses etc but the principle is what I am after here: rock wool etc could be used either.

Is there any merit in putting the insulated dpc bewteen the window frame and the concrete?

Thanks.

250882

From a professional point of view up to 5 years ago drylining should be the last resort when it came to weather proofing a house because its simply covering a problem, this is technically doing the same thing IMO.

ircoha

250882 wrote: »

From a professional point of view up to 5 years ago drylining should be the last resort when it came to weather proofing a house because its simply covering a problem, this is technically doing the same thing IMO.

What solution would you suggest then?

I am a bit puzzled as to how drylining can be regarded as weather proofing.

If the render is done correctly, using modern admixtures such as

http://www.netweber.co.uk/Servlet/Redirector;jsessionid=H3PnxnSnPkWsJ3ypxSY7Y1726JqLTHvwzs6rh72T1TnK5CYKKc1H!-1468654767?from=/Product/ProductList.jsp&action=ProdLoadFiche&random=-796297317&id=1257

The wall should be weatherproof against even driving rain.

250882

I'm a traditional kinda guy and I believe in breathable structures or at least a belt and braces approach. I think that relying completely on a water proofing system that can be poorly mixed, badly put up, can go off differently in different temperatures or where the plaster can simply skimp a bit on the quantity is a bit risky for my liking.
The theory is good but I would prefer to see the insulation on the outside. There are plenty of IAB approved externally insulated rendering systems and contractors about. Makes much more sence to have your structure on the inner leaf where its warm and dry and you can hang a TV bracket or shelf off it, also means that your not breaking the thernal envelope when floors run into the walls and with the insulation on the outside it leaves more scope to improve the details on the windows, reveals and eaves to remove cold bridging and water ingress(especially with ridges on mono-pitch roofs).
Also I personally think a thermally massive system is a better system to build with as it goes a long way to compensate for our poorly draught proofed windows and doors.

ardara1

ircoha wrote: »

Following on from some of the comments by sinnerboy and others in this thread to whom I am obliged,
http://www.boards.ie/vbulletin/showthread.php?t=2055235906,

I have been giving some consideration to the issues around thermal bridging around opes.

If one accepts that any form of quality control on cavity walls, ( filled, partial filled, pumped etc) is problematic

Why is it problematic - quality control is either there or it's not - new regs insist that it's there - full stop.

I looked at using either hollow 215mm blocks or even solid 100mm on flat and see what might work.

This design would work best in a building where you have 4 external walls with no internal walls tied into the external walls: eg garden studios and simple extensions.

Thermal bridging has biggest effect at lintels/cills/gable junctions and floor junctions - you'll still have these in constructions without internal walls.

The attached sketch shows one possible scenario on which I would welcome some comments.

The advantages for me include
1 the block work is simple, fast and std lintels etc can be used.
2 no messing with insulated dpc, closer blocks, cavity insulation etc.
3 you dont cover the window/door frames with the composite board.
4 The insulation work can be done once the building is roofed.

I appreciate there are issues around using these sorts of boards with toxic gasses etc

If there are toxic gases given off any material please let us know.

but the principle is what I am after here: rock wool etc could be used either.

Is there any merit in putting the insulated dpc bewteen the window frame and the concrete?

Are you suggesting sandwiching the insulation and DPC between the frame and the solid concrete wall?

Thanks.

There are methods written down in the regulations for measuring all thermal bridges - if the detail fails - it fails - just measure it.

muffler

ardara1, I was going to delete the post above (breach of charter) but I will leave it for now. Please read the PM I have sent.

sas

250882 wrote: »

There are plenty of IAB approved externally insulated rendering systems and contractors about.

I suppose it depends on your definition of "plenty" but there are currently only 2 IAB approved externally insulated systems rendering systems and both are Weber systems. They are extraordinarily expensive too. Approx. €150 per metre squared (ex VAT) for a u-value of 0.15.

My point being that until the price point for these systems drop (considerably) they will have minimal uptake.

ircoha

sas wrote: »

I suppose it depends on your definition of "plenty" but there are currently only 2 IAB approved externally insulated systems rendering systems and both are Weber systems. They are extraordinarily expensive too. Approx. €150 per metre squared (ex VAT) for a u-value of 0.15.

My point being that until the price point for these systems drop (considerably) they will have minimal uptake.

SAS
Thanks for the pricing.
I, too, am only aware of IAB certs for weber solutions.

For other readers of this thread this is their website.
http://www.netweber.co.uk/Servlet/Welcome

250882:
I accept your points re external insulation, an added 'advantage' of internal insulation is that it 'helps to solve' the issue of cold bridging from conventionally built foundations.

Mellor

ircoha wrote: »

The comments by Duncan are interesting, (was unable to paste them from the link.)
If this was a retro-fit job, I dont see how he can use the words 'totally eliminate'.

I don't like the way Duncan's coment were printed. He didn't actually say "eliminate bridging"

"Most Irish houses would benefit immensely from wrap-around external insulation". It is the only system that totally eliminates cold bridging in the external walls of the house.

The part in italics is whay duncan said, I am basing this on the quotations marks. The rest is the sites addition. It is not handled well as it looks like the next sentance is duncans opinion also.

As for It is the only system that totally eliminates cold bridging in the external walls of the house, this is also wrong there are many systems that can totally eliminate cold bridging. Since the website is providing a service, its best to take the facts woth a pinch of salt

BTW, The issue of cold bridging through the inner leaf into the foundation in a cavity wall is actually increased when you externally insulate. Dry lining is the only system that solces it in its basic form, cavity and external insulation need additional measures to solve it.

sas

Mellor wrote: »

This is also wrong there are many systems that can totally eliminate cold bridging. .

Out of interest, such as what? I'm particularly interested in solving the issue of a bridge between floor and wall insulation.

External insulated walls on an insulated raft such as www.isoquick.de is a great combination in my opinion. Availability is an issue here however.

ICF can pretty much also eliminate cold bridging I suppose. Is there something else you had in mind?

Mellor

Well, off the top of the aul head. ICF, well detailed internal insulation, isokorb systems, Insulated Panels etc

sas

Mellor wrote: »

Well, off the top of the aul head. ICF, well detailed internal insulation, isokorb systems, Insulated Panels etc

I have 1 issue in my head regarding ICF. Given that I'm not building a certified passive house I'm probably worrying about nothing but I may as well ask.

How much of a bridge is the following?

- You have an ICF 2 storey house.
- The ICF walls are built off the strip
- The first floor is comprised of hollowcore slabs.
- The hollow obviously bridges the internal insulation leaf and rests on the concrete core of the ICF wall.
- You remove the bridge at the floor by butting your floor insulation up against the internal leaf of polystyrene
- You remove the bridge at the wall plate by lapping your insulation over the ICF wall
- Is the fact that the hollow core creates a concrete path from inside the house to the foundations a big issue? To clarify, I'm assuming you don't insulate under to over your first storey floor.

ircoha

Following on from the first post in this thread, and taking on board Mellors comments from elsewhere to build to block sizes rather than build to exact dimensions for small lengths, would wecome some comments on whether to go 100mm on flat or 215 hollowblock.

Application is a art studio in a garden, 6m by 4m, by 2.4m to eaves of A roof, no hip, no internal block walls. Opes on 3 walls

Assuming all insulation on inside as per sinnerboy or synbeat or similiar ideas, so with no cavity wall, it seems to me that the 100mm on flat should be easier to do and perhaps be cheaper to build.

Would appreciate any opinions.

Mellor

sas wrote: »

- Is the fact that the hollow core creates a concrete path from inside the house to the foundations a big issue? To clarify, I'm assuming you don't insulate under to over your first storey floor.

Its not a problem at all. Every material offers some thermal resistance. The reason insulation is the chosen materials is because the high resistance allows thiner insulation.
A thermal bridge is an area where the thermal resistance drops below the level in the surrounding area. A thermal bridge is not nessecerily an area with no "insulation material".
The path from the hollowcore to the foundation is going to be about 3.5m, This much concrete will offer a decent level of resistance. About half the resistance of a standard wall offers.

ircoha wrote: »

Assuming all insulation on inside as per sinnerboy or synbeat or similiar ideas, so with no cavity wall, it seems to me that the 100mm on flat should be easier to do and perhaps be cheaper to build.
Would appreciate any opinions.

Im not sure about cost, but I think that 100mm on flat is the better option. It would be my prefered choice.

sas

ircoha wrote: »

Assuming all insulation on inside as per sinnerboy or synbeat or similiar ideas, so with no cavity wall, it seems to me that the 100mm on flat should be easier to do and perhaps be cheaper to build.

Would appreciate any opinions.

I thought the only way you could build in a non-cavity manner and dryline was using cavity blocks?

Can you build a single leaf wall using 100mm on the flat, then dry line and not get big problems with moisture ingress?

sas

Mellor wrote: »

Its not a problem at all. Every material offers some thermal resistance. The reason insulation is the chosen materials is because the high resistance allows thiner insulation.
A thermal bridge is an area where the thermal resistance drops below the level in the surrounding area. A thermal bridge is not nessecerily an area with no "insulation material".
The path from the hollowcore to the foundation is going to be about 3.5m, This much concrete will offer a decent level of resistance. About half the resistance of a standard wall offers.

Great, thanks for this. I'm spending too much time looking at diagrams for passive houses where the whole house is literally wrapped in insulation.

I'm not building a certified passive house and I'm finding it very difficult to satisfy myself as to where the cut off point for price versus performance is taking into account that I'll have to use some form of heating system anyway.

Mellor

Its a bit of a trade off alright.

I forgot to include in the above that the path from first floor to the foundation is more resistive than the very top spec windows. most (if not all) of the heat will have passed through the outer leaf of insulation before the foundation

250882

Ya just checked that 2 Weber systems, sorry about that. Still there are subcontractors doing the work using a weber system for a much lower price some how. alternatively what about using a cement board as an outerleaf fixed back to the structure with thermally broken rails?

sas

250882 wrote: »

alternatively what about using a cement board as an outerleaf fixed back to the structure with thermally broken rails?

Have you by any chance priced the IAB certified cement board system? It too is a tidy €100 odd + VAT a square metre.